The present invention relates to improvements in transfer arms used to move lengths of down hole tubulars between a lowered position, near ground level, and a raised position in a drilling apparatus, and to improved, self centering, hydraulically actuated tongs for making up and breaking out threaded connections in a string of down hole tubulars such as drill pipe, for example.
Drilling rigs with transfer arms and hydraulically actuated tongs are known to the art. U.S. Pat. No. Re. 26,284, issued Oct. 17, 1967 on an application of J. V. O'Neill, et al., is one early example of such a drilling rig. Such drilling rigs provide important advantages in terms of improved safety of operation, increased speed of operation, and reduced numbers of required operating personnel, as compared with conventional drilling rigs of the prior art. However, such drilling rigs have in the past suffered from certain disadvantages.
For example, one type of prior art transfer arm utilizes clamps for down hole tubulars, which clamps are rigidly mounted to the transfer arm during use. When such transfer arms are used in connection with drilling rigs having top head drives, the threaded ends of a clamped tubular can be damaged easily, as can the clamps and the transfer arm itself, if the operator is not careful to control the axial forces applied to the clamped tubular with the top head drive during make up and break out operations. Furthermore, this type of prior art transfer arm provides no adequate indication of the axial forces that are being applied to the clamped tubular, thereby further increasing the prospect of damaged tubulars, transfer arms and clamps.
In addition, it is customary to use rigid, serrated carbide inserts in transfer arm clamps, and these inserts can deeply gouge and scratch clamped tubulars during handling operations. Such gouging can materially damage a clamped tubular, for transfer arm clamps customarily grip the relatively thin walled intermediate section of a clamped tubular, rather than the tool joints.
Another drawback of the prior art relates to hydraulic tongs. Commonly available tongs are not self centering. That is, they cannot be used to center tubulars of widely differing diameters about a common clamping axis without manual adjustment. Such manual adjustment of course requires time and slows the operation of the drilling rig.